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DOE OSTI2020

Degenerate doping in B-Ga 2 O 3 Single Crystals through Hf-doping

n-type conductivity of β-Ga 2 O 3 grown from the melt is typically achieved using Sn and Si. In this paper, we experimentally and computationally investigate Hf doping of β-Ga 2 O 3 single crystals using UV–vis-NIR absorption and Hall effect measurements and hybrid functional calculations. Unintentionally-doped and Hf-doped samples with a nominal concentration of 0.5at% were grown from the melt using vertical gradient freeze and Czochralski method in mixed Ar + O 2 atmosphere. We demonstrate Hf dopants, predicted to incorporate on the octahedral GaII site as a shallow donor, achieve degenerate doping in β-Ga 2 O 3 with a measured electron concentration ~2 × 10 19 cm -3 , mobility 80–65 cm 2 V -1 s -1 , and resistivity down to 5 mΩ cm in our samples. The concentration of Hf was measured to be 1.3 × 10 19 atoms cm -3 using glow discharge mass spectroscopy on doped samples, confirming Hf to be the cause of n-type conductivity (electron concentration ~2 × 10 19 cm -3 ).

36 MATERIALS SCIENCE↗

DOE OSTI2020

Thermal conductivity of rutile germanium dioxide

Power electronics seek to improve power conversion of devices by utilizing materials with a wide bandgap, high carrier mobility, and high thermal conductivity. Due to its wide bandgap of 4.5 eV, b-Ga 2 O 3 has received much attention for high-voltage electronic device research. However, it suffers from inefficient thermal conduction that originates from its low-symmetry crystal structure. Rutile germanium oxide (r-GeO 2 ) has been identified as an alternative ultra-wide-bandgap (4.68 eV) semiconductor with predicted high electron mobility and ambipolar dopability; however, its thermal conductivity is unknown. Here, we characterize the thermal conductivity of r-GeO 2 as a function of temperature by first-principles calculations, experimental synthesis, and thermal characterization. The calculations predict an anisotropic phonon-limited thermal conductivity for r-GeO 2 of 37W m –1 K –1 along the a direction and 58W m –1 K –1 along the c direction at 300K where the phonon-limited thermal conductivity predominantly occurs via the acoustic modes. Experimentally, we measured the value of 51W m –1 K –1 at 300K for hot-pressed, polycrystalline r-GeO2 pellets. The measured value is close to our directionally averaged theoretical value, and the temperature dependence of ~1/T is also consistent with our theory prediction, indicating that thermal transport in our r-GeO 2 samples at room temperature and above is governed by phonon scattering. Furthermore, our results reveal that high-symmetry UWBG materials, such as r-GeO 2 , may be the key to efficient power electronics.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ga3B by Materials Project

Ga3B is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ga is bonded to eight equivalent Ga and four equivalent B atoms to form GaGa8B4 cuboctahedra that share corners with twelve equivalent GaGa8B4 cuboctahedra, edges with eight equivalent BGa12 cuboctahedra, edges with sixteen equivalent GaGa8B4 cuboctahedra, faces with four equivalent BGa12 cuboctahedra, and faces with fourteen equivalent GaGa8B4 cuboctahedra. All Ga–Ga bond lengths are 2.80 Å. All Ga–B bond lengths are 2.80 Å. B is bonded to twelve equivalent Ga atoms to form BGa12 cuboctahedra that share corners with twelve equivalent BGa12 cuboctahedra, edges with twenty-four equivalent GaGa8B4 cuboctahedra, faces with six equivalent BGa12 cuboctahedra, and faces with twelve equivalent GaGa8B4 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ga3B by Materials Project

Ga3B crystallizes in the hexagonal P6_3/mmc space group. The structure is one-dimensional and consists of two Ga3B ribbons oriented in the (0, 0, 1) direction. Ga is bonded in a distorted L-shaped geometry to two equivalent B atoms. Both Ga–B bond lengths are 2.31 Å. B is bonded to six equivalent Ga atoms to form distorted face-sharing BGa6 pentagonal pyramids.

36 MATERIALS SCIENCE↗